1. Field of the Invention
The present invention relates to a method of removing a surface material from a resin product having a resin substrate and the surface material formed thereon by means of coating or adhesive bonding, and an apparatus for removing the surface material.
2. Description of the Related Art
Recently, the recycling of resin products has been demanded from the viewpoints of environmental protection or resource recovery. For instance, it is noted that defective goods generated during a manufacture of bumpers or side moldings in the field of automobile industry, and resin products separately collected from scrap cars are recycled.
Most of such resin products have a structure that a paint film is coated on a resin substrate or that a different resin material is bonded onto the resin substrate, in order to improve the appearance or quality. For instance, in a resin bumper, a paint film 103 is generally formed on a surface of a resin substrate 101 through a primer layer 102 as shown in FIG. 17 illustrating a section view of the important part.
The substrate 101 is, for example, composed of materials obtained by mixing polypropylene of thermoplastic synthetic resin as a base resin, ethylene propylene rubber and talc as a filler, and the substrate 101 has a specific gravity of 0.91 to 0.98 and a thickness “t” of approx. 2 to 4 mm.
The primer layer 102 is an adhesive layer having a specific gravity of approx. 1.7 and a thickness of 10 μm and serving to strengthen the bonding strength between the substrate 101 and the paint film 103. The primer layer 102 is formed by application of a paint comprising melamine or urethane thermosetting resin as material.
In case bumpers made of resin subjected to the application processing are crushed to give pellet-shaped recycle materials, the pellet-shaped recycle materials include the above-mentioned polypropylene system resin materials constituting the resin substrate 101 and further paint chips such as the primer layer and the paint film. Therefore, when the polypropylene system resin materials containing the paint chips are subjected to a molding processing, the paint chips inhibit the liquidation of the resin materials, whereby the resultant molded product suffers from defective molding processing and shows poor appearance because of the paint chips floated on the surface of the resultant molded product. Further since there is little compatibility between the paint chips and the polypropylene system resin materials, the kneading of the paint chips and the polypropylene system resin materials does not brings about the integration of them to reduce mechanical properties of the resultant molded product.
For the reason, when the resin product subjected to the application processing is recycled, it is needed to remove the paint film from the resin product.
The method of removing a paint film is roughly divided into mechanically, physically and chemically methods. Examples of the method of removing mechanically the paint film include a shot-blast method comprising blowing down microparticulate abrasive material onto a paint film formed on a resin product using compressed air to destroy and remove the paint film or other attachment, and a screen-mesh method comprising crushing finely the resin product, fusing the product and then filtrating the fused product through a screen-mesh to remove paint film chips that are not fused and contained in the product.
The shot-blast method is excellent in view of toxicity and environmental safety because of removal of the paint film by friction and impact, whereas there are disadvantages of long processing time period, insufficient efficiency for removal of a paint film and especially difficulty in processing of a curved portion of the product. The screen-mesh method is excellent in view of toxicity and environmental safety because of removal of paint chips by filtration, but when the screen-mesh is clogged, the throughput is reduced owing to significant increase of the depressing pressure to decrease the productivity and simultaneously not to bring about sufficient removal efficiency of the paint chips, and therefore it is necessary to exchange the screen-mesh in order to avoid reduction of the production efficiency owing to clogging of the screen-mesh.
Example of the method of removing physically a paint film include a method of removing the paint film by utilizing solvent penetration phenomenon into an interface between a paint film and a substrate and a paint film and swelling phenomenon of a solvent into a paint film. The solvent includes various organic solvents including halogen-containing solvents. However, the method has disadvantages of poor environment safety due to necessity of treatment of waste liquid and relatively reduced efficiency of removing the paint film and capacity of processing it, which may deteriorate even a substrate supporting the paint film.
These methods for removing mechanically or physically a paint film show reduced efficiency of removing the paint film, and therefore the use of the resultant resin material recycled by these methods increases the production cost to bring about limitation of the application.
Example of the method of removing chemically a paint film include an organic salt method comprising breaking ether bonds in the vicinity of crosslinked structure of paint film resin using, for example, an ethanol/water mixed liquid containing an organic salt to chemically decompose the paint film and remove it.
The above-mentioned chemical method has a disadvantage in a secondary treatment such as waste liquid treatment and shows reduced processing capacity, and hence the method is not preferred in view of processing efficiency.
Further, in an example of a conventional apparatus for removing a surface material (paint film) of a synthetic resin product, a paint film is placed between a pair of rotating bodies, and cut and rubbed by the rotating bodies to peel the paint film, which is described in, for example, JA5-337941.
The conventional removing apparatus is shown in FIG. 18 illustrating its plan view, and in FIG. 19 illustrating its section view taken in I-I line. A resin product such as side molding 122 is transported between rotating bodies 123, 124 composed, for example, of synthetic resin foam by a pair of transport rollers 121 whereas a velocity “V” transporting the side molding 122 is set to be lower than a rotating velocity of the rotating bodies 123, 124. Hence, cutting and high rubbing force are applied to a paint film 122a and a double faced adhesive tape 122b to cut and peel the paint film 122a and the double faced adhesive tape 122b from the surface of the side molding 122 and simultaneously to discharge the side molding 122 outward by the pair of transport rollers 121.
In this apparatus, the resin product is brought into contact with the rotating bodies 123, 124 composed of synthetic resin foam, and hence the rotating bodies 123, 124 is subjected to brittle failure to generate powder dust, which brings about undesirable work environment. Further this apparatus is not suitable for peeling of a paint film of a resin product in the bent and curved form.
The above-mentioned problems can be applied to removal of a surface material made of different kind of resin adhesive-bonded to a surface of a resin substrate.